keep ADC reference voltage on between successive reads

To decrease the amount of time needed for PMU ADC reads, add the option
to keep the ADC reference voltage enable as its stabilization time is
the longest pole.
Also set the stabilization time to 10ms as the max defined in the
datasheet.

Signed-off-by: Vincent Palatin <vpalatin@chromium.org>

BRANCH=none
BUG=chrome-os-partner:17997
TEST=on Spring, measure EC_CMD_POWER_INFO latency and see it going from
49ms to 18ms.

Change-Id: I7ed20bcddab165250108eb9f768539b19fa251de
Reviewed-on: https://gerrit.chromium.org/gerrit/44008
Reviewed-by: Vic Yang <victoryang@chromium.org>
Commit-Queue: Vincent Palatin <vpalatin@chromium.org>
Tested-by: Vincent Palatin <vpalatin@chromium.org>

4 files changed, 27 insertions, 14 deletions

diff --git a/board/spring/board.c b/board/spring/board.c
index 8307dd9ab8..da74c966ee 100644
--- a/board/spring/board.c
+++ b/board/spring/board.c
@@ -345,8 +345,10 @@ static int power_command_info(struct host_cmd_handler_args *args)
 	struct ec_response_power_info *r = args->response;
 
 	r->voltage_ac = adc_read_channel(ADC_CH_USB_VBUS_SNS);
-	r->voltage_system = pmu_adc_read(ADC_VAC) * 17000 / 1024;
-	r->current_system = pmu_adc_read(ADC_IAC) * 20 * 33 / 1024;
+	r->voltage_system = pmu_adc_read(ADC_VAC, ADC_FLAG_KEEP_ON)
+			  * 17000 / 1024;
+	r->current_system = pmu_adc_read(ADC_IAC, 0)
+			  * 20 * 33 / 1024;
 	r->usb_dev_type = board_get_usb_dev_type();
 	r->usb_current_limit = board_get_usb_current_limit();
 	args->response_size = sizeof(*r);
diff --git a/board/spring/usb_charging.c b/board/spring/usb_charging.c
index a7f3e45728..ce864e1d9f 100644
--- a/board/spring/usb_charging.c
+++ b/board/spring/usb_charging.c
@@ -426,10 +426,14 @@ static int command_batdebug(int argc, char **argv)
 {
 	int val;
 	ccprintf("VBUS = %d mV\n", adc_read_channel(ADC_CH_USB_VBUS_SNS));
-	ccprintf("VAC = %d mV\n", pmu_adc_read(ADC_VAC) * 17000 / 1024);
-	ccprintf("IAC = %d mA\n", pmu_adc_read(ADC_IAC) * 20 * 33 / 1024);
-	ccprintf("VBAT = %d mV\n", pmu_adc_read(ADC_VBAT) * 17000 / 1024);
-	ccprintf("IBAT = %d mA\n", pmu_adc_read(ADC_IBAT) * 50 * 40 / 1024);
+	ccprintf("VAC = %d mV\n", pmu_adc_read(ADC_VAC, ADC_FLAG_KEEP_ON)
+				  * 17000 / 1024);
+	ccprintf("IAC = %d mA\n", pmu_adc_read(ADC_IAC, ADC_FLAG_KEEP_ON)
+				  * 20 * 33 / 1024);
+	ccprintf("VBAT = %d mV\n", pmu_adc_read(ADC_VBAT, ADC_FLAG_KEEP_ON)
+				  * 17000 / 1024);
+	ccprintf("IBAT = %d mA\n", pmu_adc_read(ADC_IBAT, 0)
+				  * 50 * 40 / 1024);
 	ccprintf("PWM = %d%%\n", STM32_TIM_CCR1(3));
 	battery_current(&val);
 	ccprintf("Battery Current = %d mA\n", val);
diff --git a/common/pmu_tps65090.c b/common/pmu_tps65090.c
index f5f32b1d1c..b48fbe8f2d 100644
--- a/common/pmu_tps65090.c
+++ b/common/pmu_tps65090.c
@@ -406,7 +406,7 @@ int pmu_enable_fet(int fet_id, int enable, int *power_good)
 	return EC_SUCCESS;
 }
 
-int pmu_adc_read(int adc_idx)
+int pmu_adc_read(int adc_idx, int flags)
 {
 	int ctrl;
 	int val1, val2;
@@ -415,11 +415,14 @@ int pmu_adc_read(int adc_idx)
 	rv = pmu_read(AD_CTRL, &ctrl);
 	if (rv)
 		return rv;
-	ctrl |= AD_CTRL_ENADREF;
-	rv = pmu_write(AD_CTRL, ctrl);
-	if (rv)
-		return rv;
-	msleep(20);
+	if (!(ctrl & AD_CTRL_ENADREF)) {
+		ctrl |= AD_CTRL_ENADREF;
+		rv = pmu_write(AD_CTRL, ctrl);
+		if (rv)
+			return rv;
+		/* wait for reference voltage stabilization */
+		msleep(10);
+	}
 
 	ctrl = (ctrl & ~0xf) | adc_idx;
 	rv = pmu_write(AD_CTRL, ctrl);
@@ -443,7 +446,8 @@ int pmu_adc_read(int adc_idx)
 	if (rv)
 		return rv;
 
-	rv = pmu_write(AD_CTRL, ctrl & ~AD_CTRL_ENADREF);
+	if (!(flags & ADC_FLAG_KEEP_ON))
+		rv = pmu_write(AD_CTRL, ctrl & ~AD_CTRL_ENADREF);
 
 	return (val2 << 8) | val1;
 }
diff --git a/include/pmu_tpschrome.h b/include/pmu_tpschrome.h
index 39985eea30..54da1bca57 100644
--- a/include/pmu_tpschrome.h
+++ b/include/pmu_tpschrome.h
@@ -89,6 +89,8 @@ enum FASTCHARGE_TIMEOUT {
 #define ADC_IFET6	12
 #define ADC_IFET7	13
 
+/* do not turn off voltage reference */
+#define ADC_FLAG_KEEP_ON	0x1
 
 /**
  * Clear tps65090 IRQ register
@@ -188,8 +190,9 @@ int pmu_low_current_charging(int enable);
  * Read ADC channel
  *
  * @param adc_idx        Index of ADC channel
+ * @param flags          combination of ADC_FLAG_* constants
  */
-int pmu_adc_read(int adc_idx);
+int pmu_adc_read(int adc_idx, int flags);
 
 /**
  * Handles interrupts from tpschrome